Aetos Installation Manual
9.4
Alarm Switch
When some device (any CAN bus device) reports an error condition, like some
engine parameter outside limits or a sensor failure, an output signal will be
raised. This alarm line can be used to trigger some other device, an alarm
light on the instrument panel, for example.
Figure 32 illustrates schematics for small load connected to pin 8. When
alarm is on, optocoupler internaly connects the line to ground (GND) and
closes the circuit – the current starts flowing through the load. The load
must be externally powered with the system bus voltage.
1
5
6
9
8
Alarm
+12 V
Max load
50 mA
Optocoupler
inside
Figure 32:
Alarm switch schematics with the load on the line.
Figure 33 illustract solution for a larger load. This load must be connected
via relay and the circuit must be protected with a flyback diode. (Some relays
have this diode already built-in.) When alarm is on, the circut is closed by
optocoupler and coil in the relay gets energized. This, in turn, activates the
relay switch and closes the load circuit.
1
5
6
9
8
Alarm
+12V
+12 V
Relay and
flyback diode
Load
Optocoupler
inside
Figure 33:
Alarm switch schematics with the relay solution for larger loads.
38
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Kanardia
2019–2020